Morphological Study of the Gastrointestinal Tract of Larimichthys
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ZOOLOGIA 35: e25171 ISSN 1984-4689 (online) zoologia.pensoft.net RESEARCH ARTICLE Morphological study of the gastrointestinal tract of Larimichthys crocea (Acanthopterygii: Perciformes) Hameeda Kalhoro 1,2, Shengli Tong 1, Lei Wang 1, Ying Hua 1, Josie Ancella Volatiana 1, Qingjun Shao 1 1Aquaculture Nutrition Laboratory, College of Animal Sciences, Zhejiang University. Hangzhou 310058, China. 2Department of Fresh Water Biology and Fisheries, Faculty of Natural Sciences, University of Sindh Jamshoro. Jamshoro 76080, Pakistan. Corresponding author: Qingjun Shao ([email protected]) http://zoobank.org/E6F123A8-B168-4AB7-A45F-F0FD375051A1 ABSTRACT. The present study aimed to investigate the macroscopic and histological structure of the gastrointestinal tract (GIT) of Larimichthys crocea (Richardson, 1846). It consists of esophagus, stomach regions, pyloric caeca, intestinal regions, and rectum. Sixteen tubular light yellowish pyloric caeca of similar sizes were observed in all individuals. The digestive wall consists of mucosa, submucosa, muscularis, and adventitia. No major differences appeared in the structure of the tunica, epithelial cell types, connective tissues and musculature glands of L. crocea GIT. The mucosal epithelia in the oesophagus has longitudinal branched folds with frontward and hindmost zones. The gastric tunica mucosa has a characteristic folded structure and can be divided into three regions. The intestinal tunica mucosa is characterized by villi structures and numerous mucus-secreting cells. Mucus-secreting goblet cells were strongly positive to AB at pH 2.5 in the oesophagus (excluding gastro-oesophageal junction) and intestine mucosal regions, which indicates an abundance of carboxylate mucins. The sur- face epithelia of the gastric mucosa is PAS-positive and AB-negative. SEM examination revealed that cells in the epithelium of the esophagus have an unbroken apical layer and goblet cells. The intestinal coefficient (IC) of L. crocea was 0.80 ± 0.21, consistent with a carnivorous or omnivorous habit. Our study adds the knowledge of the digestive system of L. crocea and might be useful in the management of L. crocea stocks. KEY WORDS. Anatomy, epithelial mucins, gastrointestinal tract, intestinal coefficient, large yellow croaker. INTRODUCTION The large yellow croaker, Larimichthys crocea (Richardson, 1846), known as drums or croakers in reference to the repetitive Morphological studies help in understanding the rela- drumming echoes they make, belong to Sciaenidae (Ramcharitar tionship between physiological and biochemical functions et al. 2006). This important carnivorous marine fish species is and molecular mechanisms. The gastrointestinal tract (GIT) cultivated in many Asian countries, particularly China (Feng of fish has shown a remarkable diversity of morphological and Cao 1979). The ontogenetic development of the digestive and functional traits, particularly in connection with unusual tract of L. crocea was briefly described by Mai et al. (2005). nutritional behaviors, body shape and sex (Díaz et al. 2008b, Young fish start out with a simple, indistinguishable GIT that Kapoor et al. 1975). There have been many contributions on changes during development according to the environmental the morphology of the GIT structure of fish, including marine, conditions and prey availability (Govoni et al. 1986). Function- freshwater and estuarine species (Murray et al. 1994, Park and al differences in the GIT of fish are reflected in their capacity Kim 2001). Furthermore, due to various structural differences to digest, absorb and assimilate chemical compounds and are in the GIT of fish, nutritional studies have been the focus of also associated with the developmental situation (Dabrowski most research in the field. For instance, past research has tried 1984). In aquaculture, studying the anatomical and histological to correlate morpho functional characters of the GIT of fish with characteristics of the GIT of fish may help to understand the their nutritional habits and behaviors, the results of which are development of pathological conditions, to devise nutritional important to commercial fish management. formulations and promote the management of L. crocea stocks ZOOLOGIA 35: e25171 | DOI: 10.3897/zoologia.35.e25171 | November 1, 2018 1 / 9 H. Kalhoro et al. in aquaculture. The primary goal of the present study was to ± 1.01 cm), mean standard length (22.78 ± 1.00 cm), intestinal describe the macroscopic and histological organization of the length (18.29 ± 4.76 cm) and intestinal coefficient (0.80 ± 0.21 GIT of L. crocea. IC). The GIT of L. crocea consists of the esophagus, stomach regions, pyloric caeca, intestinal regions, and rectum. The short MATERIAL AND METHODS esophagus connects the pharyngeal cavity with the stomach. The u-shaped stomach is a muscular sack between the esophagus and Twelve mature L. crocea were obtained from the Marine the anterior intestine and sits behind the liver. Sixteen tubular Fisheries Research Institute of Zhejiang Province, Zhoushan, light yellowish pyloric caeca of similar sizes were observed in all China. After being anesthetized with tricaine methanesulfonate, individuals. The short intestine extends from the pyloric region MS 222; Sigma Chemical Co. solution by using a dosage of 100 of the stomach to the rectum and can be divided into anterior, mg L−1, the fish were euthanized via a longitudinal incision middle and posterior regions (Fig. 1). through their ventral side. The length of the intestine was measured to the nearest millimeter, using a tape measure and the intestinal coefficient (IC) was calculated using the equation IC = IL/SL (Angelescu and Gneri 1949). The segmental tissue fragments were removed after dissection and immediately processed for histological, histochemical and scanning electron microscopic studies. Sliced tissue fragments from the separated GIT were fixed in 10% formalin (for 24 hours). After fixation, tissues were repeatedly washed in 70% ethanol and dehydrated via ethanol series. Then tissues were cleared in xylene and em- bedded using paraffin wax at 56–58 °C. Sections were sliced at 5 µm using a 820 HistoStat Reichert Rotatory Microtome (Reichert Technologies, NY, USA). After routine histological procedure, dewaxed sections were stained with haematoxy- lin – eosin (HE) solutions. Stained slides were examined and photographed under Olympus B202 microscope (Olympus Optical, Ltd, Tokyo, Japan). The fragments were preserved and processed similarly to Figure 1. Photograph of the L. crocea gut illustrating: (ES) esophagus, the procedure described above. Five to seven µm sections were (CS) cardiac stomach, (FS) fundic stomach, (PS) pyloric stomach, prepared and stained in Periodic acid-Schiff (PAS), Alcian blue (PC) pyloric caeca, (AI) anterior intestine, (MI) mid intestine, (PI) (AB pH 2.5) and PAS+AB pH 2.5 to identify the neutral and acidic posterior intestine, and (RE) rectum. Scale bar = 7 cm. mucins respectively. The sample processing method for scanning electron mi- croscopy is described elsewhere in detail (Kalhoro et al. 2017). Histology and scanning electron microscopy (SEM) In brief, tissues were fixed in 4% paraformaldehyde and 2.5% glutaraldehyde in phosphate buffer (pH 7.0) (for 24 hour at 4 The digestive wall consists of mucosa, submucosa, muscu- °C). After fixation, tissues were post-fixed for 1–2 hours in 1% laris, and adventitia. No major differences were observed at the osmium tetroxide (pH 7.0) and desiccated in a graded ethanol structure of the tunic structure, epithelial cell types, connective sequence placed in a mixture of alcohol and isoamyl acetate (v: tissues and musculature glands in the GIT of L. crocea with v = 1:1) about 30 minutes, then shifted to pure isoamyl acetate respect to other observed individuals. The tunica muscularis for overnight. Finally, tissues were washed and desiccated in of the esophagus appears rigid, forming two muscular layers, inner longitudinal layer, and outer circular layer. The tunica Hitachi Model HCP – C critical-point dryer through liquid CO2. Desiccated samples were coated with gold-palladium in Hitachi muscularis in the stomach is also rigid and forms two smooth Model E-1010 ion sputter for 4–5 minutes and observed in SEM muscular layers, inner circular layer, and outer longitudinal layer. (TM-1000, Hitachi, Japan). The mucosal surface in the proximal intestine has numerous elongated and deep folds lined by simple columnar goblet cells. In the distal intestine, the folds are fewer and shorter, contain- RESULTS ing large numbers of goblet cells, and no glands in the mucosa Gross anatomy and submucosa. The absence of muscularis mucosa prevented a distinct separation between the lamina propria and the sub- The body measurements obtained to L. crocea (n = 12) mucosa. The tunica muscularis in the intestine is organized in were: body weight (198.79 ± 20.36 g), total body length (25.83 2 / 9 ZOOLOGIA 35: e25171 | DOI: 10.3897/zoologia.35.e25171 | November 1, 2018 Morphology of large yellow croaker Figures 6–8. Photograph illustrating the transverse section of oeso- phagus containing mucus cells (arrow), lamina propria and lumen Figures 2–5. Photograph of L. crocea GIT illustrating the general (6–7 stained with Hematoxylin and eosin stain). (8) Mucus-secreting organization: (2) transversal section of the oesophagus, note the cells in the anterior part of the oesophagus (arrows) possessing muscular possessing an inner longitudinal layer and an outer circular neutral and acidic carboxylated